PROJECT SUMMARY/ABSTRACT The proposed research focuses on investigating the role of astrocyte reaction in Alzheimer's disease (AD). Much of AD research has focused on the two pathological hallmarks of the disease -amyloid plaques and neurofibrillary tangles- and their effects on neurons and synapses. Reactive astrocytes are universally present in neurodegenerative diseases, and in AD they react to plaques and tangles, but whether they contribute to neurodegeneration or are neuroprotective remains uncertain. The applicant's research strategy aims at a deep phenotyping of astrocytes in AD mouse models and the human AD brain. The hypothesis to be tested is that astrocyte phenotype changes along the course of AD, from neuroprotective to neurotoxic, and perhaps senescent astrocytes in the end-stage. Importantly, this project builds upon prior observations made by the applicant using stereology-based quantitative methods in human brain specimens, while moving towards experimental grounds and extending his skillset including astrocyte purification methods, RNA-seq, bioinformatics, astrocyte-specific manipulations in AD mouse models with viral-mediated gene delivery, novel histological methods (i.e. cyclic immunofluorescence, array tomography), and biochemical methods (i.e. sequential protein extraction, synaptoneurosome preparations). The candidate's research environment is ideal for the project. The Massachusetts General Hospital and the Harvard Medical School are a nurturing atmosphere for trainees, and have multiple core facilities. The MassGeneral Institute for Neurodegenerative Diseases and the Massachusetts Alzheimer's Disease Research Center are first rank infrastructures devoted to research on AD and other neurodegenerative diseases. The candidate's mentoring team is composed of a world-class AD researcher (Dr. Bradley Hyman), a renowned neuropathologist (Dr. Matthew Frosch), and an early PhD investigator with expertise in AD mouse models and molecular biology tools including viral-mediated gene transfer (Dr. Eloise Hudry). The advisory team will contribute with expertise in viral-mediated gene transfer (Dr. Xandra Breakefield), astrocyte biology and pathology (Dr. James Goldman), and RNA-seq and astrocyte synaptic functions (Dr. Beth Stevens). The candidate's training plan includes both career development lectures on relevant topics (i.e. grant writing, scientific communication, and training in responsible conduct of research), as well as a series of intensive Harvard Catalyst courses that are pertinent to the proposed research (i.e. Certificate in Applied Biostatistics, Introduction to Omics Research, Introduction to RNA-seq). The combination of a nurturing research environment, experienced mentoring and advisory teams, and a comprehensive training plan, with allow the applicant to fulfill his short and long-range career goals, which are deciphering the role of astrocyte reaction in AD and transitioning towards an independent clinician scientist position, respectively.